linux-kernel - Re: [PATCH v2 2/4] phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom chips

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Date:   Fri, 2 Dec 2016 10:47:46 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     kishon <kishon@...com>, robh+dt <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 2/4] phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom
 chips

On 12/01/2016 12:42 AM, Vivek Gautam wrote:
> On Tue, Nov 29, 2016 at 4:44 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> On 11/22, Vivek Gautam wrote:
>>> +     }
>>> +
>>> +     /*
>>> +      * we need to read only one byte here, since the required
>>> +      * parameter value fits in one nibble
>>> +      */
>>> +     val = (u8 *)nvmem_cell_read(cell, &len);
>> Shouldn't need the cast here. Also it would be nice if
>> nvmem_cell_read() didn't require a second argument if we don't
>> care for it. We should update the API to allow NULL there.
> Will remove the u8 pointer cast.
>
> Correct, it makes sense to allow the length pointer to be passed as NULL.
> We don't care about this length. Will update the nvmem API, to allow this.
>
> Also, we should add a check for 'cell' as well. This pointer can be
> NULL, and the first thing that  nvmem_cell_read does is - deference
> the pointer 'cell'

It would be pretty stupid to read a cell and pass NULL as the first
argument. I imagine things would blow up there like we want and we would
see a nice big stacktrace.

>>> +     } else {
>>> +             reset_val |= CLK_REF_SEL;
>>> +     }
>>> +
>>> +     writel_relaxed(reset_val, qphy->base + QUSB2PHY_PLL_TEST);
>>> +
>>> +     /* Make sure that above write is completed to get PLL source clock */
>>> +     wmb();
>>> +
>>> +     /* Required to get PHY PLL lock successfully */
>>> +     usleep_range(100, 110);
>>> +
>>> +     if (!(readb_relaxed(qphy->base + QUSB2PHY_PLL_STATUS) &
>>> +                                     PLL_LOCKED)) {
>>> +             dev_err(&phy->dev, "QUSB PHY PLL LOCK fails:%x\n",
>>> +                     readb_relaxed(qphy->base + QUSB2PHY_PLL_STATUS));
>> Would be pretty funny if this was locked now when the error
>> printk runs. Are there other bits in there that are helpful?
> This is the only bit that's there to check the PLL locking status.
> Should we rather poll ?
>

I'm just saying that the printk may have the "correct" status but the
check would have failed earlier making the printk confusing. Perhaps
just save the register value from the first read and print it instead of
reading it again? Polling would probably be a better design anyway?
Hopefully the status bit isn't toggling back and forth during those
100-100us though, which may be the case here and that would explain why
it's not a polling design.

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